The subject matter of this invention relates to mononuclear Cu.sup.II and Zn.sup.II phenoxyl complexes and mono- and binuclear radical complexes thereof, methods for the preparation of the complexes and the use of the phenoxyl radical complexes as catalysts in oxidation reactions with oxygen, and in particular, for the oxidation of primary or secondary alcohols.
It is known that aldehydes can be produced by dehydrogenation or by oxidation of primary alcohols; in the first case, the by-product that forms is molecular hydrogen, in the second case, the by-product is water.
With the use of enzymatic redox systems, it is possible to oxidize different substrates, which leads to the formation of hydrogen peroxide as a coupling product. The oxidase which, as a rule, is flavin-dependent oxidizes the substrate, and the reduced form of the enzyme is reoxidized by molecular oxygen while forming hydrogen peroxide. For example, according to the German Patent No. DE-A 4,231,767, an enzyme with oxidase activity, such as glucose oxidase, in combination with the oxidizable substrate can be used as a bleaching system in bleaches and detergents. According to the U.S. Pat. No. 5,234,827, hydrogen peroxide can be produced in the aqueous phase, using a short-chain alcohol, an extracellular alcohol oxidase which is free from catalase activity. Drawbacks of the enzymatic systems for oxidation reactions and/or for the production of hydrogen peroxide are the restrictions with respect to the admissible pH and temperature range, the high substrate specificity which often limits the versatile use, and the risk of deactivating and thus reducing the activity of the enzyme as a result of an irreversible oxidation by means of the hydrogen peroxide that forms.
It is known that in its active form, galactose oxidase which catalyzes the oxidation of primary alcohols to form aldehydes and H.sub.2 O.sub.2 contains a Cu.sup.II ion which is bonded to a tyrosyl radical that is S-modified in the ortho position. The galactose oxidase thus contains a radical cofactor--see, for example, N. Ito et al. in J. Mol. Biol. (1994), Vol. 238, p. 794, and R. M. Wachter et al. in J. Amer. Chem. Soc. (1996), Vol. 118, p. 2782. Using the structural models of Cu.sup.II phenoxyl for the active form of glucose oxidase as a starting point, Y. Wang, T. D. P. Stack et al. in Science (1998), Vol. 279, p. 537, introduced mononuclear Cu.sup.II compounds with quadridentate ligands which, under aerobic conditions, catalytically oxidize benzyl alcohols and allyl alcohols to form the corresponding aldehydes or ketones while at the same time forming hydrogen peroxide. According to an article in Chem. & Eng. News of Jan. 26, 1998, p.9, one of the specially active Cu.sup.II compounds, the preparation of which, however, is highly time- and cost-consuming, is a compound of the following formula: ##STR3##
An object of the present invention is to identify additional Cu.sup.II phenoxyl complexes and Cu.sup.II phenoxyl radical complexes which can be obtained therefrom and which catalyze oxidation reactions with molecular oxygen. The new Cu phenoxyl radical complexes should be readily accessible.
Another object of the invention is to provide Cu phenoxyl radical complexes that make it possible to oxidize alcohols other than those so far oxidized with the previously known complexes.
A further object of this invention is to identify areas in which the substrate-catalyst systems can be used and in which the hydrogen peroxide that is formed in situ is purposefully utilized.